Magneto-inductive flow meters utilize the principle of electrodynamic induction for measuring volume flow rate. Charge carriers of the medium moved perpendicularly to a magnetic field induce a voltage in measuring electrodes likewise arranged essentially perpendicularly to the flow direction of the medium. This induced voltage is proportional to the flow velocity of the medium averaged over the cross section of the pipe; it is thus proportional to volume flow rate.
A magneto-inductive flow meter is manufactured and sold by the firm of Endress+Hauser under the label Promag 53.
Magneto-inductive flow meters are used in many ways in the food and pharmaceutical industries. Especially in these applications, a regular cleaning of the entire measuring system composed of the flow meter, including the pipelines, is necessary. One possibility for the cleaning is to uninstall the measuring device from the pipeline system and, following deinstallation, clean it separately. This method of cleaning is very complicated for the user and, to some extent, not even practical. Recently, a technique for cleaning has become preferred, in the case of which a deinstallation of the measuring device is no longer necessary. This method of cleaning is known in automation technology under the label CIP (Clean in Place). For such a method, in particular cases, strict regulations have been put in place by the pertinent authorities (e.g., FDA, Food and Drug Administration). A CIP (Clean in Place) method involves sending a cleaning liquid through the measuring system. The cleaning liquid effects an appropriate cleaning of the measuring device including the pipeline system.
Due to the different physical properties of the cleaning medium in comparison to the medium being measured, considerable fluctuations in the measurement signal can arise. In the face of such fluctuations, measured values can no longer be reliably obtained. The summing of the measured values in a totalizer is no longer possible. Individual measured values, so called outliers, can completely corrupt the results of the totalizing.
As a rule, an evaluation electronics is only designed for a medium being measured, that remains the same, with constant physical characteristics.
One possibility for avoiding the problems arising in the cleaning process, is to blank out the measurement signal during the cleaning process. This could be done over a fixedly predetermined time interval. A fixedly predetermined time interval is, however, impractical since the duration of the cleaning process depends on the specific application, and, consequently, can have varying lengths. The time interval would, therefore, have to be adjustable manually, this being an extremely inconvenient matter for the user.
A further disadvantage, which results from blanking out of the measurement signal during the cleaning process, is that there then has been no opportunity to determine the amount of cleaning liquid used. Frequently, it is desired, or even required by regulation, to keep the amount of the cleaning liquid being used likewise constant. In this way, it can be proved that the cleaning procedure was performed according to regulation. For this determination, however, additional equipment would be necessary.